2.8 Beta - Save all images "invalid path"?
this isn't broken or incomplete, it does work!!
What you haven't done is SAVE the files YOURSELF first!
Once you have done this the first time, every other time you press the Save All Images button, it WILL Save ALL your Images!!
Got me stuck for a bit too, but you just need to give it a path first, then you're good to go :]
Cheers
Wayne